US 2004/0084127 A1 discloses a glass reinforced cementitious board reinforced by a glass reinforcement sheet, and a hydrophilic coating material on the binder coated glass fibers.
U.S. Pat. No. 7,429,544 discloses a facing material having a randomly oriented mesh filament network with a first binder, an aqueous secondary binder resin having a viscosity sufficient to partially penetrate the open mesh filament network, and an aqueous coating wherein the aqueous coating includes a filler, acicular man-made fibers and a binder of fairly low glass transition temperature.
U.S. Pat. No. 6,524,679 discloses a glass reinforced cementitious board having a cementitious core. The core is formed by a hydraulic cementitious compound constituted as a slurry. The slurry is overlaid and underlayed by glass reinforcement sheets for encasing the core. Further, the outwardly facing surfaces of the sheets are overlaid or coated by applying a thin film of additional slurry to cover and avoid exposed glass fibers of the sheets. The glass fiber profiles are coating with a thin film but are visible under the thin film. Heat is applied to hasten slurry hydration and drying to form a hardened cementitious core, while excess slurry water dissipate by evaporations as water vapor through the sheets to dry the core.
U.S. Pat. No. 4,378,405 discloses a glass reinforced cementitious board for which the cementitious core is formed by vibrating the a hydraulic cementitious compound constituting a slurry while the slurry is overlaid and underlayed by glass reinforcement sheets for encasing the slurry. Vibrations impel the slurry through pores of the sheets to form a thin film of cementitious slurry to cover and avoid exposed glass fibers and to provide a smooth cementitious surface on the thin film.
Further, U.S. Pat. No. 4,378,405 discloses it is difficult under ordinary conditions to bond a cementitious slurry adequately to glass fibers of the sheets that serve as substitutes for conventional paper facings for encasing a slurry.
Further, the glass fibers of the sheet bond together by a binder on the glass fibers. A hydrophobic binder resists wetting by the slurry to resists formation of a thin film of slurry over the glass fibers. A hydrophilic binder on the glass fibers is moisture absorptive to collect moisture and promote unwanted mold and bacterial growth.
Water content of the hydraulic cementitious compound resists bonding to hydrophobic glass fibers and a hydrophobic binder on the glass fibers. However a hydroscopic binder or hydrophilic binder, such as one from a group of polar (polar chemical bonding) acrylic binders or polyvinyl alcohol binder on the glass fibers absorbs and retains moisture, wherein the retained moisture would support undesirable mold or bacterial growth on a cementitious board. Further, a hydroscopic or hydrophilic polar binder loses binder tensile strength by becoming soft and limp when wetted by the cementitious slurry
Further, the hydraulic cementitious compound can contain additives that increase the slurry viscosity, making it difficult to bond to the binder covered glass fibers. Further, to provide a water-resistant core that resists moisture absorption, the hydraulic cementitious compound can constitute a water-resistant additive, such as wax-asphalt emulsion, siloxane, styrene/acrylate polymer or silicone.
Apparatus suitable to manufacture the glass reinforced cementitious board is described in each of US 2004/0084127; U.S. Pat. Nos. 7,049,251; 6,524,679 and 4,378,405, wherein US 2004/0084127 discloses a fiber reinforcement sheet treated by spraying for example with a substance to enhance wetting and adhesions characteristics thereof, and a conveyor belt supporting a slurry of a cementitious board and the fiber reinforcement sheet. However, residues of the substance in the cementitious board would contribute to undesired hydroscopicity or hydrophobicity of the cementitious board.
U.S. Pat. No. 7,049,251 discloses a top sheet and a bottom sheet with slurry therebetween and exposed in a drying oven which accelerates drying by increasing the rate of evaporation of excess water.
It would be desirable for reinforcement sheets to be hydrophilic at beginning contact with a slurry of a hydraulic cementitious compound to encourage slurry wetting, slurry spreading and forming an adequate bond with the slurry, and thereafter to be hydrophobic while embedded in a core of a cementitious board to discourage moisture absorption and retention.